transparency crape ring saturn peculiarities von barnard e e (1 Ergebnisse)

Soft cover. Zustand: Good. Original offprint Astronomy and Astro-physics, No. 102, W.W. Payne & George E. Hale.(the previous incantation of this journal for the preceding ten volumes was the Sidereral Messenger). 9X6" (two illustrations), 4pp. Inscribed "from the author". Condition: nice copy, Good/Very Good, though a little tender. Scarce. "Barnard saw the gegenschein in 1882, not aware of earlier papers by Theodor Brorsen and T. W. Backhouse.  In 1889 he observed the moon Iapetus pass behind Saturn's rings. As he watched Iapetus pass through the space between Saturn's innermost rings and the planet itself, he saw a shadow pass over the moon. Although he did not realize it at the time, he had discovered proof of the "spokes" of Saturn, dark shadows running perpendicular to the circular paths of the rings. These spokes were doubted at first, but confirmed by the spacecraft Voyager 1."--Wikipedia __+__"The conjecture that Barnard saw spoke shadows on Iapetus contradicts modern scientific understanding of where spokes occur. It is otherwise consistent with the normal optical depth of spokes, their increased contrast at small ring opening angles, and their ability to cover long radial distances and broad areas. It appears to be consistent with observations of transitory dark markings on the C ring in the late 1880s as well as with a similar case in 1992. See Figure 13 for an observation made by Stroobant a few months after the eclipse of Iapetus. However, even if this interpretation is wrong, I urge that two aspects of Barnard's observation are significant. He saw Iapetus begin to fade before it reached the C-D ring boundary. He also saw Iapetus become fainter than Enceladus too soon. Apparently, a condition existed in the inner ring system on 1-2 November 1889 that does not, for whatever reason, exist now."-- James Bryan, "E.E. BARNARD AND THE ECLIPSE OF IAPETUS IN 1889", in Journal of Astronomical History and Heritage, 10(1), 31-48 (2007).